Transmission of pictures or views



TRANSMISSION OF PICTURES OR VIEWS Feb. E7, 1931.

Filed Sept. 30,

Inventor: R a9 D. KeLL,

H is Attorney Patented Feb. 17, 1931 NITED STATES RAY I). BELL, OI SCOTIA, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC COMIPANY,

A CORPORATION YORK TRANSMISSION OF PICTURES OB VIEWS Application filed September 80, 1929. Serial No. 896,080.

My invention relates to the tra nsmissionof pictures or views and has for 1ts principal object the provision of an improved picture receiving apparatus of the cathode ray type a which may be utilized to receive pictures transmitted by a transmitting apparatus ncluding a rotatable perforated scanning (llSC or the like.

In the past, different types of picture rere ceiving apparatus, including a cathode ray device have been utilized. In the utilization of such devices a stream of electrons is projected from one end of a vacuum tube on a fluorescent screen at the other end where 1t 35 produces a bright spot, the intensity of the cathode ray being modulated in accordance with the shade of the successive elemental areas of the picture to be produced and the movement of the ray being controlled by an electrostatic or an electromagnetic field which causes it to scan or sweep over the receiving screen. The movement of the cathode ray or the scanning of the receiving screen is usually effected by means of magnetic or electrostatic fields of dilierent frequencies applied to the ray in difl'erent directions by means of suitable electrodes. For this purposetwo oscillators operating at different frequencies are sometimes employed. This method of scanning, however, is not suitable for use in picture receiving apparatus which is utilized in connection with transmitting apparatus including a rotatable scanning disc or the like, for the reason that it is impossible to' establish the proper relation between the rotational speed of the disc and the frequency of the oscillators. In accordance with my invention this dificulty is obviated by the provision of an improved cathode ray picture receiving apparatus which may be readily synchronized with the rotatable disc or other movable part of the picture transmitting apfrom the cathode 13 is projected upon the and 19 and 20 is effected by means of a contact sidered in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

The drawing illustrates a picture receiving apparatus wherein myinvention has been embodied.

This apparatus includes a radio receiver 10 through which electrical impulses modulated in accordance with the shade of the successive elemental areas of the transmitted picture are applied to the input circuit of a space discharge device 11. The output circuit of this device includes a source of current shown as a battery 12 the cathode 13 and the anode 14 of a vacuum tube 15. Between the cathode and anode of the vacuum tube 15 is interposed a perforated shield 16. This tube is provided at its left hand end with a fluorescent screen 15'. A stream of electrons screen through the shield 16 and the anode 14 and is caused to move through a predetermined c cle of movements by a pair of electrodes I; and 18 and a pair of electrodes 19 and 20.

It will be noted that the electrodes 18 and 19 are connected to the anode 14 and to the cathode of the discharge device 11. The electrode 17 is arranged to be connected to the cathode 13 through the battery 12, a battery 22 and a space discharge device 21. The electrode 20 is arranged to be connected to the cathode 13 through the battery 12, a space discharge device 23 and the battery 22. A condenser 24 is connected in parallel with the device 21 and a condenser 26 is connected in parallel with the device 23. Variation in the potential applied between the two pairs of electrodes 17 and 18 device arranged to be drlven by a motor 27. This contact device includes a slip ring 28 connected to the battery 22, a commutator 29 arranged to successively complete a circuit which includes the condenser 26 and a source of current 31, and a commutator 32 arranged a to complete a circuit which includes the condenser 24, and a source of current 34;. The apparatus is grounded at a point 35 between the batteries 12 and 22.

The operation of the apparatus will be readily understood if it be assumed that no potential is applied between the pairs of electrodes 17 and 18 and 19 and 20. Under these conditions there is applied between the oathode and anode of the cathode ray tube 15 a potential which is modulated in a well known manner in accordance with the shade of the successive elemental areas of the transmitted picture. Due to this potential, a stationary cathode ray is projected on the screen 15, this ray producing a spot of light which is stationary and changes its brilliancy in accordance with otential applied between the oathode 13 and the anode 14. Movement of the cathode ray to scan the screen 15 and produce a picture thereon is effected by means including the contact or commutator device which is driven by the motor 27.

The commutator 29 is provided with a plurality of insulation segments interposed between the conductor segments. As this commutator is rotated the condenser 26 is successively charged and discharged, this condenser being charged substantially instantaneously by the battery 31 when the brush of the commutator 29 is in contact with a conductive segment, and being discharged at a substantially constant rate through the device 23 when the brush of the commutator is in contact with an insulation segment. Due to the charging and discharging of the condenser 26, a variable potential is applied between the electrodes 19 and 20 and the cathode ray is moved back and forth in one direction for example, horizontally, across the screen 15'.

In order to scan the screen 15', it is of course essential that the cathode ray be moved also in a vertical direction. This result is produced by means of the commutator 32 which is provided with a single insulation segment and a single conductive segment. When the brush of the commutator 32 is in contact with the conductive segment, the condenser 24 is charged substantially instantaneously by the battery 34 and when the brush of this commutator is on the insulation segment the battery 24 is discharged at a substantially constant rate through the device 21. Due to the charging and discharging of the condenser 24:, a variable potential 1s applied between the electrodes 17 and 18 and the cathode ray is moved across the screen 15' in a vertical direction. As a result of this movement the ray successively sweeps over the area of the screen 15.

The use of a contact or a commutator device for controlling the movement of the ray has the important advantage that the scanning of the screen 15 by the ray may be readily synchronized with the movement of the scanning beam produced by the well known Nipkow disc or apparatus of like character. The apparatus utilized for controlling the movement of the cathode ray is comparatively inex ensive and is much simpler than that hereto ore utilized for this purpose.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A picture receiving apparatus including a vacuum tube provided with a screen, with means including a cathode and anode for directing a stream of electrons on to said screen, and with pairs of electrodes for controllin the direction in which said stream is app led to said screen, a plurality of condensers connected respectively to control the potential difl'erences of the pairs of electrodes, means for discharging said condensers at predetermined rates, means for charging the condensers comprising a source of current and a plurality of contact devices in circuit therewith arranged to o erate at different frequencies having a xed relation with one another, and a common driving means for said contact devices.

2. A picture receiving apparatus including a vacuum tube provided with a screen, with means including a cathode and anode for directing a stream of electrons on to said screen and with pairs of electrodes for controlling the direction in which said stream is applied to said screen, a plurality of condensers each connected to one of the pairs of elec trodes, a plurality of space discharge devices arranged to discharge the respective condensers at difierent predeterminedrates, condenser charging means comprising a source of current and a plurality of contact devices arranged to operate at different frequencies having a fixed relation with each other and a common driving motor for said devices.

In witness whereof, I have hereunto set my hand this 27th day of September, 1929.

RAY D. KELL. 

